This image from video provided by the FBI, shows Aaron Alexis moves through the hallways of Building #197 at the Washington Navy Yard on Monday, Sept. 16, 2013, in Washington, carrying a Remington 870 shotgun. Alexis, a 34-year-old former Navy reservist and IT contractor, shot and killed 12 people inside a Navy Yard building last week before being killed in a shootout with police. (AP Photo/FBI)

WASHINGTON (AP) — Washington Navy Yard gunman Aaron Alexis left a note saying he was driven to kill by months of bombardment with extremely low-frequency radio waves, the FBI said Wednesday in a disclosure that explains the phrase he etched on his shotgun: “My ELF Weapon!”

Alexis did not target particular individuals during the Sept. 16 attack in which he killed 12 people, and there is no indication the shooting stemmed from any workplace dispute, said Valerie Parlave, assistant director in charge of the FBI’s Washington field office. Instead, authorities said, his behavior in the weeks before the shooting and evidence recovered from his hotel room, backpack and other belongings reveal a man increasingly in the throes of paranoia and delusions.

“Ultra-low frequency attack is what I’ve been subject to for the last 3 months, and to be perfectly honest that is what has driven me to this,” read an electronic document Login to read more